Based on work supported by the parent application concerning the role of FGF family members in thymic epithelium (TE) development and function, we have proposed the hypothesis that multi-potential pharyngeal endodermal progenitor cells persist within the adult thymus and in other endodermally-derived organs and tissues. Within the thymus, these cells would play a central role in maintaining medullary epithelial heterogeneity, while in extrathymic, endodermally-derived tissues, these progenitor cells could retain the capacity to support thymopoietic environments. Because of the commingled nature of the epithelia within the thymus and in other epithelial tissues, traditional approaches to analyze gene expression are not feasible and in situ approaches are too labor and time intensive to rapidly survey the expression of a large number of genes, Furthermore, this latter approach would not identify novel or unanticipated gene products. The activities proposed here will develop the infrastructure and experimental approaches necessary to test several postulates of this hypothesis. Specifically, we wish to employ laser capture micro-dissection to recover thymic tissue components and to utilize the recovered RNA to probe the profiles gene expression by defined compartments of thymic epithelium. This approach has been used successfully in several studies of the thymic environment, thus speaking to the utility of the approach, but has not been widely employed due to the novelty of the required instrumentation. This application requests support to bring state-of the art technologies to explore the character and regulation of the thymic microenvironment. The information gained is likely to provide new insight into several important areas of thymus biology, including the regulation of thymic epithelial development, which in turn is likely to be centrally involved in the maintenance of self tolerance and the control of age-related thymic involution. [unreadable] [unreadable]